Preparation of reaction products of tetrafluorohydrazine with polyvinylfuroate, useful as energetic binders for propellants



United States Patent 6) PREPARATION OF REACTION PRODUCTS F TET- RAFLUOROHYDRAZINE WITH PGLYVINYLFU- ROATE, USEFUL AS ENERGETIC BINDERS FOR PROPELLANTS Anthony J. Passannante, Metuchen, N.J., assignor to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Aug. 16, 1961, Ser. No. 134,799

9 Claims. (Cl. 260-885) This invention relates to a process for preparing highenergy oxidizing polymer binders by an addition reaction of tetratiuorohydrazine (N F with polyvinylfuroate.

The N F adducts of polyvinylfuroate when suitably prepared to contain a high proportion of NF groups, e.g. 2 to 4 NF groups and preferably 3 to 4 NF groups per monomeric unit are useful in high-energy rocket propellant systems and serve to increase the specific impulse (Isp) beyond that obtainable with polymeric binders lackns oxidizing oup Attempts to add N R; to polymeric compounds have shown that certain difiiculties can arise in obtaining adequate contact of reactants and from formation of undesired decompositionproducts including some which may be explosive. On the other hand, direct addition of N F to a preformed polymer has advantages in curtailing the handling of materials.

It has now been found in the development of the present invention that polyvinyl furoate can be satisfactorily solvated with a solvent for a safe andnearly complete saturation of the furan ring double bonds in polyvinyl furoate by NF groups. For complete saturation, four difluoramino (NF groups are added per furan ring in the polyvinylfuroate (PVF) according to the following equation:

Various lowand high-molecular weight PVF polymers commercially available and such as prepared by reaction of polyvinyl alcohol with furoyl chloride C H OCOCl have been used for the reaction with N F The PVF polymers contain 11 multiple of the recurring units (I); so that for the higher molecular weight PVF polymers, n is a higher integer. In general, the high-molecular weight PVF has a molecular Weight in the range of 20,000 to 200,000, and the low-molecular weight PVF has a molecular weight in the range of 2,000 to 20,000.

The low molecular weight PVF and mixtures of lowwith high-molecular weight PVF are more soluble than the high-molecular weight PVF in the better solvents found suitable for the N F reaction, e.g. particularly acetonitrile, chloroform, and acetonitrile-carbon tetrachloride.

For the addition of N F to PVF, enough N F is charged into the reaction zone containing the PVF reactant, to supply an excess of 1 N F per PVF unit or per furan ring. Thus, for N1 saturation of the furan rings at least about 6 parts by weight of N F are supplied per 4 parts by weight of the PVF.

Conditions found generally suitable for the PVF-N F reaction are reaction temperatures in the range of about 100 to 130 C., N F pressures in the range of about 250 to 500 p.s.i.a., and reaction periods in the range of 1 to 20 hours. These conditions can be varied, e.g. a reaction ice period with higher reaction temperature and better contact: of. the reactants-in. the reactionmixtu-re.

A, typical experimental procedure is described in. th following example:

Example A feed' charge of-0123 g. ofpolyvinylfuroate (20,000 molecular weight) is dissolved in 101111. of acetonitrile and the solution is placed in a-25 m1; stainless-steel bomb. After degassing the solution at -196 CL, liquid N 3.2 g. N F are introduced intothe solution in the bomb. The reactor is closed, warmed up, then heated at 125 C. for 4 hours. The unreacted N F is removed. The resulting liquid solution is filtered and the solvent is evaporated from the filtrate to obtain 0.55 g. of-difiuoraminatedpolyvinyl furoate as residual product. Analysis: N, 12.36%; F, 34.7%; F/N ratio=2/1'. This product contained'47% NFQ compared to a theoretical 60.2% for tetrakis-NF addition to the furan rings in the PVF, but higher NF- contents were obtained by' extending the time usingthe same solvent and reaction temperature.

In a subsequent run using N F at approximately 400 p.s.i.a. in acetonitrile,. a higher uptake ofabout 1 /2. moles N F per monomer unit was obtained. The difluoraminated PVF product obtained was a light tan tobrown rubbery material easily dispersed in acetonitrile. The shock sensitivity of this product was in the-range 0512 to 2.0 kg. inches. The analysis of the product and comparison to theoretical requirements are given in the following table.

A further improved reaction was carried out using acetonitrile as diluent to obtain at least reaction of the double bonds in the PVF, shown as follows:

TABLE 2 N :F4, Addition to PVF Percent N Percent F Percent NF: FIN Ratio Product 42. 6 15. 67 58. 3 1. 98/1 Studies on varying conditions have shown that 4 hours reaction at C. and about 400 p.s.i.a. N F pressure gave optimum results.

Thus, using a polyvinyl furoate in which the recurring unit is principally [C H OOCC H O] the N F reaction can be carried out as shown therewith to obtain a PVF- N F reaction product in which the recurring unit is of similar order of magnitude principally A number of solvents have looked promising for use as reaction media, but there are differences in the effectiveness of the solvents. Acetonitrile acts well as a solvent but it may form some contaminants. However, these contaminants can be removed by extraction with an alcohol, e.g. methanol. Acetonitrile may be used in a mixed solvent, e.g. with CHCl but again care must be taken to keep down reaction that forms contaminants. Other solvents, such as dioxane, chloroform, sulfolane and acetone, may be used in this reaction of PVF with N F depending upon the amount of difluoramino groups desired in the product.

These solvents tend to react with N F at high temperatures and long contact times and are therefore not suitable as solvents in areas where these conditions are necessary for attaining a high degree of addition of N F to the PVF.

The PVF-N F adducts are generally more soluble in CH CN and CHCl and less so in CCl The higher molecular weight polymers tend to be less soluble in all solvents than the lower molecular weight product. These relationships indicate that these NF -containing polymers can be purified by selective extraction and precipitation. By further purification the PVF-N F adduct is made reasonably stable. It is adequately stable for 60 hours at 60 C.

The PVF-tetrakis (NF adduct has a calculated heat of formation value, AH 298 K. of -187 Kcal./mol., which puts it in the class of high energy binders.

PVF (NF adducts containing about NE; by weight were found to have advantages of higher density (e.g., 1.64 g./cc.) and stability (low gas loss at C.) compared to other polymer adducts. They are useful as binders with other oxidizers in the form of solids, binders, or liquid plasticizers, and high-energy fuels. For example, a propellant composition containing 25% tris (NF adduct of PVP units [CH CHOOCCJ-I (NF O], as binder, 25% tetrakis (NF butane, 7% B, and 43% C (NO has a specific impulse of 283.8 seconds. Other formulations of this type using the tris and tetrakis NF adducts of PVP also have high Isp values above 270 seconds.

Modifications in the method of preparing the PVF-NF binder and its use will be apparent to those skilled in the art within the scope of this invention.

.What is claimed is:

1. Process for preparing N F adducts of polyvinyl furoate which comprises solvating the polyvinylfuroate in a liquid solvent of low reactivity selected from the group consisting of acetonitrile, chloroform, carbon tetrachloride, and mixtures of acetonitrile with a halogenated hydrocarbon, and reacting the thus solvated polyvinyl furoate with admixed N F at a reaction temperature in the range of about C. to C. under pressure and with an amount of the N 1; to chemically combine from 2 to 4 NF groups with double bonds of each furan nucleus in the polyvinylfuroate and recovering the resulting polyvinylfuroate-N F adduct product containing the NF groups.

2. A process as defined in claim 1, wherein the solvent is acetonitrile.

3. A process as defined in claim 1, wherein the solvent is chloroform.

4. A process as defined in claim 1, wherein the solvent is a mixture of CH CN and a halogenated hydrocarbon.

5. A process as defined in claim 1 in which the polyvinylfuroate-N F adduct product is purified by extracting alcohol-soluble impurities from said product. 7

6. Process for preparing difluoraminated polyvinylfiuroate which comprises, dissolving polyvinylfuroate having a molecular weight in the range of 2,000 to 200,000 in liquid acetonitrile, reacting thus dissolved polyvinylfuroate in solution with N F introduced into said solution at a reaction temperature of about 100 to 130 C. under a pressure of about 250 to 500 p.s.i.a., at least about 6 parts by Weight of the N F being introduced into said solution per 4 parts by weight of the polyvinylfuroate in the solution, carrying out the reaction for a period to form the difiuoraminated polyvinylfuroate product, and recovering said product.

7. A process as defined in claim 6, wherein the acetonitrile solvent is mixed with chloroform.

3. A process as defined to claim 6, wherein the acetonitrile solvent is mixed with carbon tetrachloride.

9. A process as defined in claim 6, wherein the recovered product is purified by extracting alcohol-soluble impurities therefrom.

References Cited Farber: Astronautics, August 1960, pages 34, 40, and

JOSEPH L. SCHOFER, Primary Examiner.

HARRY WONG, JR., Assistant Examiner. 

1. PROCESS FOR PREPARING N2F4 ADDUCTS OF POLYVINYL FUROATE WHICH COMPRISES SOLVATING THE POLYVINYLFUROATE IN A LIQUID SOLVENT OF LOW REACTIVITY SELECTED FROM THE GROUP CONSISTING OF ACETONITRILE, CHLOROFORM, CARBON TETRACHLORIDE, AND MIXTURES OF ACETONITRILE WITH A HALOGENATED HYDROCARBON, AND REACTING THE THUS SOLVATED POLYVINYL FUROATE WITH ADMIXED N2F4 AT A REACTION TEMPERATURE IN THE RANGE OF ABOUT 100*C. TO 130*C. UNDER PARESSURE AND WITH AN AMOUNT OF THE N2F4 TO CHEMICALLY COMBINE FROM 2 TO 4 NF2 GROUPS WITH DOUBLE BONDS OF EACH FURAN NUCLEUS IN THE POLYVINYLFUROATE AND RECOVERING THE RESULTING POLYVINYLFUROATE-N2F4 ADDUCT PRODUCT CONTIANING THE NF3 GROUPS. 